1. Field of the Invention
The present invention relates to a heat-curable resin composition that has excellent curability, and yields a cured product that exhibits excellent heat resistance, light resistance and ultraviolet light resistance, has good strength, and is resistant to discoloration and particularly yellowing upon heating, and therefore offers excellent reliability. The present invention also relates to a premolded package for an LED or solar cell that is molded from a cured product of the above composition, and an LED device that uses such a premolded package.
2. Description of the Prior Art
Achieving the required level of reliability for the encapsulating materials used for encapsulating semiconductor and electronic devices is becoming more and more difficult as the devices become thinner and smaller, and have increasingly higher outputs. For example, semiconductor elements such as LED or LD (laser diode) are small, emit a bright colored light with good efficiency, and because they are semiconductor elements, do not suffer from lamp blowout, exhibit excellent drive performance, and have superior durability to vibration and repeated ON/OFF switching. As a result, they are widely used for all manner of indicator lights and light sources.
Polyphthalamide resins (PPA) are currently widely used as one of the materials for packages that use these types of optical semiconductor elements such as LED.
However, the dramatic progress currently being made in optical semiconductor technology has resulted in marked increases in the output of these optical semiconductors and a significant shortening of the wavelength. As a result, in semiconductor devices such as photocouplers that are capable of emitting or receiving high-energy light, semiconductor element-encapsulating resins or cases that use a conventional PPA resin as a colorless or white material tend to suffer marked deterioration upon prolonged use of the device, resulting in various problems such as color irregularity, peeling of the encapsulating resin, and reduction in the mechanical strength of the device. Effectively resolving these problems is highly desirable.
More specifically, JP 2,656,336 B (Patent Document 1) discloses a B-stage epoxy resin composition for encapsulating an optical semiconductor, which includes an epoxy resin, a curing agent and a curing accelerator as the structural components of the encapsulating resin, and in which the composition is composed of a cured product of a resin composition in which the above structural components are mixed together uniformly at the molecular level. In this case, a bisphenol A epoxy resin or bisphenol F epoxy resin is mainly used as the epoxy resin, although the document mentions that other resins such as triglycidyl isocyanate may also be used. However, in the examples of Patent Document 1, the triglycidyl isocyanate is only added in a small amount to a bisphenol epoxy resin, and according to investigations conducted by the inventors of the present invention, the resulting B-stage epoxy resin composition for encapsulating a semiconductor suffers from yellowing, particularly when left to stand for long periods at high temperature.
Furthermore, the use of a triazine derivative epoxy resin within an epoxy resin composition used for encapsulating a light-emitting element has been disclosed in JP 2000-196151 A (Patent Document 2), JP 2003-224305 A (Patent Document 3), and JP 2005-306952 A (Patent Document 4). However, if a high-brightness LED is mounted on a package or the like prepared using this type of resin composition, then the package tends to discolor upon prolonged illumination of the LED.
In addition to the documents mentioned above, other known publications relating to the present invention include Patent Documents 5 to 7 and Non-Patent Document 1 listed below.
[Patent Document 1] JP 2,656,336 B
[Patent Document 2] JP 2000-196151 A
[Patent Document 3] US 2003/0132701 A1
[Patent Document 4] JP 2005-306952 A
[Patent Document 5] JP 3,512,732 B
[Patent Document 6] JP 2001-234032 A
[Patent Document 7] JP 2002-302533 A
[Non-Patent Document 1] Electronic Packaging Technology, 2004. 4 edition